Lab talk

May 30, 2012

Liquid-like carbon nanotubes improve polymer composites

Typically, carbon nanotube (CNT)/polymer composites have been fabricated by incorporating CNTs into polymer hosts using either solvent-free or solution processing techniques. Solvent-free processing methods, including melt compounding and in situ bulk polymerization, often suffer from high mixture viscosity, which can yield poorly dispersed CNTs in the polymer matrix. Solution-based techniques promote better homogeneous dispersion of CNTs, but the solvents used can induce structural defects within the matrix during processing, which lowers the mechanical, thermal and electrical properties of the composite. Such methods are also unsuitable for insoluble polymers.

Now, an international research group led by scientists from China and Australia has developed an elegant approach that overcomes these difficulties. The technique uses liquid-like CNTs to fabricate homogeneous polymer-based composites through solvent-free processing. Amino-functionalized CNTs behave like a viscous liquid, which is easier to handle and process.

Protective layer

Liquid-like CNTs are individually exfoliated into a liquid mixture of epoxy resin, curing agent and catalyst under mechanical agitation and ultrasonication before curing (see image). Meanwhile, the surface amino groups on the CNTs serve as an activated polyamine curing agent and react with the epoxide groups to form a polymer "protective layer". This prevents the fully dispersed CNTs from re-aggregation during epoxy curing and results in a strong interface with the surrounding matrix.

As a result, the molecular-level integration of liquid-like CNTs into epoxy shows significant improvements in the overall mechanical properties of epoxy composites relative to those composites containing solid CNTs due to poor dispersion and weak interface of the latter.

About the author

Dr Ying-Kui Yang is associate professor of polymer materials science and Chutian Scholar at Hubei University, China. His research interests are focused on the fabrication of nanocarbon-polymer composites, flexible/stretchable conductors and energy storage/transfer materials. Prof. Yiu-Wing Mai holds a University Chair at the University of Sydney, Australia, and is Fellow of the Royal Society and the Royal Academy of Engineering. His major research interests are fracture mechanics and advanced materials. Prof. Xiao-Lin Xie is Dean of the School of Chemistry and Chemical Engineering at Huazhong University of Science and Technology, China. His current research activities cover the science and engineering of polymer-based composites, liquid crystalline polymers and functional polymer materials.